There are two distinctive types of imaging systems in contemporary nuclear medicine. One type is represented by the gamma scintillation cameras (GSCs), the so-called "position sensitive" continuous-area detectors, and the other one by Positron Emission Tomography (PET) scanners. The first type deals with the single photon gamma emitters enabling planar static and dynamic studies as well as Single Photon Emission Computed Tomography (SPECT), while the second type enables tomographic imaging of the positron emitters, i.e., PET studies. Both techniques enable direct imaging of biochemical processes "in vivo" (especially, the PET technique) and the study of physiological processes and dysfunctions in a quantitative manner. However, imaging systems for both types of techniques are rather expensive. The costs involved for these systems have greatly contributed to the overall expenditures for contemporary high technology medicine, which is a serious problem even in the most developed countries (e.g., U.S.A., Japan, United Kingdom, Germany, and France). Besides the commercial problem, there is a scientific problem: that of enabling simultaneous application (in the same person) in a short sequence of single photon gamma and positron emitters.
Thus far, it seems that there has been no satisfactory solution for a unique design to image both single photon and positron emitters. Contemporary PET scanners with their circumference arrangements of BGO crystals (efficient absorbers of high photon energies of 511 KeV emanating from positron emitters), i.e., of small opposing detectors connected with coincidence electronics, are designed to detect exclusively the positron emitters in a tomography mode. Position sensitive area detectors of the GSC type are made with the thin NaI(TI) crystals for optimal imaging detection of the low energy single photon gamma emitters; here, optimal imaging detection assumes an optimal spatial resolution for energies up to 150 KeV, with a shortage of the detection efficiency for medium and higher energies of single photon gamma emitters (250 and 360 KeV) being significantly reduced. Such a reduced efficiency makes the detection of high energy photon emissions, such as the ones of 511 KeV from positron emitters, difficult or impossible. There is a design of a system made of opposing position sensitive area detectors in coincidence mode fitted with thick (1 inch (in.) for increased efficiency) NaI(TI) crystals, to be used only for tomographic detection of positron emitters (due to the intolerantly worse spatial resolution for lower energies of single photon emitters). The fact, however, that this is also an imager aimed at serving PET exclusively, as well as that in such a system, the optimal spatial resolution for PET has not still been achieved due to the inherent "parallax" error, emphasizes and indicates the need for an imaging system which solves the above mentioned problems.
References which may be of interest include the following, which concern the design of position sensitive GSC type detectors:
U.S. Pat. Nos: 3,011,057; 3,745,345; 3,921,000; 3,943,336; 4,057,725; 4,700,074; PA1 H. O. Anger: Rev. Sci. Inst., 29, 27, (1958); PA1 H. O. Anger: Nucleonics, 21, 10, 56, (1963); PA1 H. O. Anger and D. H. Davis Rev. Sci Inst., 35, 6, 693, (1964); PA1 H. O. Anger: IEEE Trans. Nucl. Sci., 13, 3, 380, (1966); and PA1 G. Muehllehner, et al.: J. Nucl. Med., 21, 771, (1980). PA1 G. Muehllehner, et al.: IEEE Trans. Nucl. Sci., 23, 1, 528, (1976); PA1 J. S. Karp, et al.: IEEE Trans. Nucl. Sci., 33, 1, 550, (1986); and PA1 J. S. Karp, et al.: J. Nucl. Med., 31, 617, (1990). PA1 M. E. Phelps, et al.: J. Nucl. Med.; 16, 210, (1975); PA1 M. E. Phelps, et al.: IEEE Trans. Nucl. Sci., 23, 516, (1976); PA1 Z. H. Cho, et al.: J. Nucl. Med., 18, 840, (1977); PA1 M. E. Phelps, et al.: J. Nucl. Med., 19, 635, (1978); PA1 E. J. Hoffman, et al.: IEEE Trans. Nucl. Sci., 33, 1, 452, (1986); PA1 E. J. Hoffman, et al.: J. Nucl. Med., 3, 29, 983, (1988).
In addition, the following references concern the design of PET scanners based on position sensitive imaging detectors fitted with thick (e.g., 1 in.) NaI(T1i) crystals:
Finally, the following references concern the design of "classic" PET scanners, mostly fitted with a circumference arrangement of BGO crystals:
J. A. Sorenson and M. E. Phelps: Physics in Nuclear Medicine Sec. Edit., Saunders (1987).